package org.streets.commons.util;

import java.io.ByteArrayOutputStream;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * A collection of utility methods for working on GZIPed data.
 */
public class GZIPUtils {
    
    private static final Log log = LogFactory.getLog(GZIPUtils.class);    
    private static final int EXPECTED_COMPRESSION_RATIO = 5;    
    private static final int BUF_SIZE = 4096;
    
    /**
     * Returns an gunzipped copy of the input array. If the gzipped input has
     * been truncated or corrupted, a best-effort attempt is made to unzip as
     * much as possible. If no data can be extracted <code>null</code> is
     * returned.
     */
    public static final byte[] unzipBestEffort(byte[] in) {
        return unzipBestEffort(in, Integer.MAX_VALUE);
    }
    
    /**
     * Returns an gunzipped copy of the input array, truncated to
     * <code>sizeLimit</code> bytes, if necessary. If the gzipped input has
     * been truncated or corrupted, a best-effort attempt is made to unzip as
     * much as possible. If no data can be extracted <code>null</code> is
     * returned.
     */
    public static final byte[] unzipBestEffort(byte[] in, int sizeLimit) {
        try {
            // decompress using GZIPInputStream
            ByteArrayOutputStream outStream = new ByteArrayOutputStream(
                    EXPECTED_COMPRESSION_RATIO * in.length);
            
            GZIPInputStream inStream = new GZIPInputStream(
                    new ByteArrayInputStream(in));
            
            byte[] buf = new byte[BUF_SIZE];
            int written = 0;
            while (true) {
                try {
                    int size = inStream.read(buf);
                    if (size <= 0)
                        break;
                    if ((written + size) > sizeLimit) {
                        outStream.write(buf, 0, sizeLimit - written);
                        break;
                    }
                    outStream.write(buf, 0, size);
                    written += size;
                } catch (Exception e) {
                    break;
                }
            }
            try {
                outStream.close();
            } catch (IOException e) {
            }
            
            return outStream.toByteArray();
            
        } catch (IOException e) {
            return null;
        }
    }
    
    /**
     * Returns an gunzipped copy of the input array.
     *
     * @throws IOException
     *             if the input cannot be properly decompressed
     */
    public static final byte[] unzip(byte[] in) throws IOException {
        // decompress using GZIPInputStream
        ByteArrayOutputStream outStream = new ByteArrayOutputStream(
                EXPECTED_COMPRESSION_RATIO * in.length);
        
        GZIPInputStream inStream = new GZIPInputStream(
                new ByteArrayInputStream(in));
        
        byte[] buf = new byte[BUF_SIZE];
        while (true) {
            int size = inStream.read(buf);
            if (size <= 0)
                break;
            outStream.write(buf, 0, size);
        }
        outStream.close();
        
        return outStream.toByteArray();
    }
    
    /**
     * Returns an gzipped copy of the input array.
     */
    public static final byte[] zip(byte[] in) {
        try {
            // compress using GZIPOutputStream
            ByteArrayOutputStream byteOut = new ByteArrayOutputStream(in.length
                    / EXPECTED_COMPRESSION_RATIO);
            
            GZIPOutputStream outStream = new GZIPOutputStream(byteOut);
            
            try {
                outStream.write(in);
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    e.printStackTrace();
                }
            }
            
            try {
                outStream.close();
            } catch (IOException e) {
                if (log.isDebugEnabled()) {
                    e.printStackTrace();
                }
            }
            
            return byteOut.toByteArray();
            
        } catch (IOException e) {
            if (log.isDebugEnabled()) {
                e.printStackTrace();
            }
            return null;
        }
    }
    
}
